An angular vibrator is not only widely used for the calibration of dynamic characteristics of all kinds of angular vibration (angular displacement, angular velocity and angular acceleration) sensors, but also used for angular vibration environment test of various products.
At present, a large displacement angular vibrator, whose angular displacement is more than 180 degrees, usually adopts the structure that is based on a brushless motor. PENG Jun, HE Qun, XUE Jing-feng and SUN Hao published a paper with the title of Low Frequency Standard Angular Exciter in Metrology & Measurement Technology in 25(6) of 2005. A low frequency angular vibrator is mainly composed of a mechanical system, a control system, a measuring system and a signal processing system. The mechanical system is mainly composed of a main spindle, a table, an air bearing, a grating and a motor. The sensor to be calibrated is installed on the table, and the motor is used as a driving component for driving the rotation of the main spindle, and the air bearing takes advantage of homogenizing effect produced by gas film and attains the goal of improving the rotary precision and reducing the friction. The control system is mainly composed of a torque motor, a controller and an amplifying circuit. The controller is equipped with an electric current loop, a conversion loop, a speed loop and a position loop to improve the control performance. The computer is used to control the DAC to produce sinusoidal signals with different frequencies and amplitudes, which are sent to the control system, then the angular vibrator is driven to produce a sinusoidal angular motion with a certain frequency and amplitude. In the measuring system, the angle movement measured by a circular grating is used to be a feedback quantity for control, and a multi-channel data acquisition module is used for collecting electrical signal produced by grating and the sensor to be calibrated. Finally, the sensitivity and phase shift of the sensor to be calibrated are obtained in the signal processing system based on the calculation of the angle movement measured by the circular grating. The maximum output angular displacement (single peak value) of the system is more than 180 degrees.
The disadvantage of this low frequency angular vibrator lies in:
1. The low frequency angular vibration can only be produced in the angular vibrator, which is restricted by the response time of the motor.
2. The torque output from the angular vibrator will ripple because of the cogging effect in the motor itself, which will definitely effect on the output waveform of the vibrator although a brushless DC torque motor is used. If a brush DC torque motor is used, the output waveform from the angular vibrator will become worse because of the influence of the friction in the motor.